Power press process for forming lightweight refractory articles, and articles so made



Aug. 2, 1966 J. R. PARSONS POWER PRESS PROCESS FOR FORMING LIGHTWEIGHT REFRACTORY ARTICLES. AND ARTICLES SO MADE Filed Feb. 11, 1964 FIE- E United States Patent Illinois Filed Feb. 11, 1964, Ser. No. 343,982 13 Claims. (Cl. 264-43) The present application is a continuation-in-part of Ser. No. 189,282, filed April 23, 1962, now Patent No. 3,150,989.

The invention relates to a power press process for forming insulating refractory shaped articles such as bricks, wedges, keys, arches, and the like. More particularly the invention relates to a method of dry and semi-dry pressing of lightweight aggregate into shaped articles, and to the articles so made.

The problem of producing a uniform power-pressed brick has long presented difficulties in the manufacture of brick. Pressure is applied top and bottom to a slightly damp mixture of clays but pressure lines develop parallel to the direction of the applied pressure. The result is pressure toward the mold box sides and a decrease of pressure downward which forms the brick. To aid in transmitting this pressure downward crushed brick or grog is sometimes used, but, even with these additives, brick of about four inches in thickness are all that are normally produced, when using presses that can deliver 10,000 lbs. per square inch of pressure. Studies of encapsulated pressure gauges which are inserted in mold cavities prior to power pressing of conventional mixes prove that differential pressures exist due to the bridging of aggregates and the inequality of slippage within the mass caused by friction and lack of plasticity under pressure.

In view of the problems presented in normal drypressing of heavy fire brick, these problems become compounded when insulating brick are produced by the power press method. Early experiments using lightweight aggregates and the normal procedure of clay binders show excessive crushing of the lightweight aggregates near the top and bottom plates where the pressure was applied.

In trying to solve these problems and develop a pressable lightweight insulating brick, I have developed a process that greatly extends the range and usefiulness of power pressed equipment, thus permitting the use of more complicated dies, with more elaborate configurations, and the extended usage of removal pins and inserts. All of these are in useful ranges that far exceed anything now available.

Another object and advantage of the invention is the provision of a method of power pressing crushable lightweight insulating aggregate into shaped articles without substantially crushing the aggregrate and thus increasing the density.

Another object of the invention is to provide a method of power pressing crushable lightweight insulating aggregate into shaped articles wherein a portion of the shaped article becomes dense and strong and another portion remains of the original low density.

Other objects and advantages of the invention will become apparent as the following detailed description progresses, reference being had to the accompanying drawings diagrammatically showing different embodiments of my invention.

"ice

In accordance with one embodiment of the invention a uniform lightweight shaped refractory article is attained by mixing a lightweight insulating aggregate (called a base aggregate) with another and more readily crushable aggregate (called a sacrificial aggregate), preferably also with a bonding agent such as clay; placing the mixture in a mold of the desired shape, and pressing the mixture into the shape of the mold at a pressure high enough to crush the second material but not so high as to crush the first material; and then firing the shaped article to bring about a ceramic bond, such as a glassy bond from the clay bonding agent.

This embodiment of the invention is illustrated in FIG. 1 and FIG. 2 showing a schematic representation of the process wherein the mixture of base :and sacrificial aggregates are shown by numeral =1 in a press box 2. The piston 3 and the piston 4 in the press box 2 move together in the direction of the arrows as shown in FIG. 2, to press the aggregate under sufficient pressure to crush the sacrificial aggregate but not the base aggregate. This gives a uniform lightweight pressed refractory article such as a brick.

In another embodiment of the invention wherein shaped articles are produced having increased strength at a predetermined portion, the base aggregate as well as the sacrificial aggregate is crushed at a portion or zone of the mixture but only the sacrificial aggregate is crushed at the remainder of the mixture. This is illustrated in FIGS. 3 and 4 showing a pressing process, called bank pressing, wherein the aggregate is loaded unevenly or banked; and in FIGS. 5 and 6 wherein the uneven pressure is also obtained by the shape of the contact surface of the piston 3.

I call the crushable aggregate a sacrificial aggregate, because it is destroyed by compacting or pulverizing as the brick is pressed, but in the destruction of this sacrificial aggregate the base aggregate is moved down and into place, uniformly. The base insulating aggregate is not subject to excessive crushing because it is surrounded by the sacrificial aggregate.

Any lightweight aggregate can be used as the base uncrushed aggregate by selecting a sacrificial aggregate which is more readily crushable. From a practical point of view, however, the base aggregate should have sufficient crushing strength so as to maintain its original dimension-al state at pressures of at least 10 lbs. per square inch. Likewise, for suitable insulating qualities it should have a density of less than 50 lbs. per cubic foot.

The preferred base aggregates are those having higher crushing strength than aggregates made from expanded perlite. However, in accordance with this invention, it is possible to use the expanded perlite as the base aggregate provided some more easily crushable aggregate, such as diatomaceous earth, is used as the sacrificial aggregate.

The preferred base or uncrushable aggregates are expanded blast furnace slag, expanded shale such as Haydim, and fired foam aggregate obtained by firing a kaolin, kyanite, zircon flour or alumina foam, particularly such foams made by the process disclosed in my copending application Serial No. 189,282, filed April 23, 1962, now US. Patent 3,150,989.

The sacrificial aggregate can be any aggregate which is more readily crushable than the base aggregate. Preferably, also, it should be a lightweight aggregate having bulk density of less than 50 lbs. per cubic foot, since,

even though it is crushed into a denser state, it isadvisable to start with a material of low density.

A sacrificial aggregate which I have found particularly suitable for the above mentioned base aggregate is expanded perlite. Even though perlite introduces a flux into the insulating brick, it still serves satisfactorily in most instances.

A completely non-fluxing sacrificial aggregate can be made from unfired foam clay. Suitable unfired foam clay and foamed alumina, kyanite, and zircon flour are disclosed in my copending application Serial No. 189,282

except that instead of firing the foams as disclosed in the application to temperatures of 3000 F. and above, the

mesh willweigh '16 pounds percubic foot, vwhilethe same aggregate through mesh 011528 mesh will weigh- 23 pounds per cubic foot. Y

The following. examples relate to the power pressing of grog into the finalshaped bricks.

Example I Percent.

Fired (2550 F) clayfoam'aggregate inch? on 10 mesh) (made in @accordance withEX- ample XI of S.N.- 189,282) 42 Fired (2550 F.) clay foam aggregate (10 mesh and fines) 14 Bond clay (raw kaolin) 33 Sacrificial aggregate (expanded lperlite) 11:

Water content ,14 to 24 This brick was power pressed ina-a pressure range of 42 to 79 pounds per square inch .to .a standard.

7 9" X 4 /2" X 2 /2"'sizebrick .and fired to cone 14.

those made by US. Patent 2,676,892). and other porous or cellularnrefractory materials.

It is again mentioned that any of the sacrificial light.- weight aggregates can also be a base aggregate, and the. base aggregates can be the sacrificial aggregate, provided that two aggregates are selectedone ,of which requires substantially higher pressure to crush than the other. i

In carrying out the present process requiring the pressing of the mixture and base sacrificial aggregates, I prefer to use sacrificial aggregates Whichretain water as a part of the mineral itself, such as perlite and vermiculite, since this water helps in the pressing operation and gives a more uniform product.

In producing the refractory insulating mixture or grog for pressing, a bonding agent'is generally necessary to bind the lightweight aggregate together and provide a point contact bond under pressure The bonding agents include bonding clays such as kaolin, fire clays, ball clays, and wad and sagger clays. Occasionally small amounts of bentonite will improve the bonding qualities of the grog.

The following table discloses a suitable range of the cellular or porous lightweight aggregate formulae for the manufacture of insulating brick.

' TABLE I Percent Coarse cellular base aggregate or inch to 10 mesh) 0 to 60 Fine cellular base aggregate (10 mesh and fines) 10 to 60 Raw binding clays 0 to 70 Sacrificial aggregate 10 to 25 Water 1 to 1 Preferably 20-70 In general the base aggregate is present either coarse. or fine, but preferably both, and is present in greater 1 amount than the sacrificial aggregate. The water is present in amount to give pressability to the composition but not sufiicient to make it a slurry. The sacrificial aggregate 'is preferably of smaller size particles than the base The brick upon firing to cone 14 showed only 2 percent total shrinkage. weight of the pressing mixture.

Example ll.

Percent Fired kyanite foam aggregate (6,mesh and fines) (madesin accordance with Example XIV-of S.N. 189,282) 47 Raw kaolin. V 47. Perlite (expanded); 6 Water, content 8 to 32" This mixturewas pressed in a range of 28 to 148' pounds per square inch'and fired .at 25.00 F. The

resulting brick was found to be satisfactory and wascomparable in 'shrinkage'to the brickiof Example 1.

I Examp le lll Percent Fired alumina foam taggregate,(8 mesh and fines) (made-in accordance with Example.

XIII of SN. 189,282) 46 Raw kaolin 46' Perlite (expanded) 8 Water. content .15 to 20 The pressure range for this mixture-was found to be 28 'to 48 poundsiper square vinchFt-o provide a satisfactory brick. The pressed mixture was suitably-fired to give a lightweight refractory brick.

Water content 15 This mixturewas power pressed and fired .to cone 14. The pressure rangeto provide a satisfactory product was to 141 pounds per square inch. At this firing, the brickshowed only 2 percent; shrinkage. When tested for service by reheating to 2800* F., the brick developed only v1 percent shrinkage.

The brick ofthe preceding four examples has excel-- lent spall resistance while the presently known insulating refractory brick have, poor spall resistance,- since Where thin walls of plastic clay are fired-to a semi-vitreous or vitreous state to obtain commercial strength, they .are

is very important in obtaining proper press behavior; It

appears necessary to obtain .the maximum die travel to insure strong edges and corners for the insulating brick. For example, a cellular aggregate through 4 mesh on 10 very sensitive to heat shock and 'tendto crack easily.-

The present inventionovercomes this. weakness by combining a coarse,"stable, pre-firedinsulating aggregate or grog (accompanied by the sacrificial aggregate) with a plastic clay of substantially finer particle size than the pre-fired aggregate, and then power pressingthisimixture. The clay is- 1001'mesh which is substantially The water. content is. .based on the finer than even the lines of the pre-fired aggregate. When this brick is fired, the firing is only to provide bonding in the brick. This firing gives two distinct glassy phases in the finished product, one glassy phase being the bond of the pre-fired aggregate, and the other being the glassy bond of the bonding clay. It is desired that the aggregate or grog and the clay have slightly different bonding behavior so that when heat shock develops, a continuous break cannot develop through both the aggregate and the bond. Where a crack develops in the bond, it travels until it meets a piece of coarse aggregate and the crack can go no further and stops.

It has also been found that the refractory insulating aggregates of this invention can be given improved stability above their original firing temperature so as to decrease the amount of undesirable shrinkage by the addition of specific elements or compounds such as sulfur, sodium fluoride and calcium fluoride. These additives will improve the shrinkage characteristics of the clay over a wide range of temperatures to 3000 F.

In the examples given the foam aggregate, wherever used, can be any of the fired foam aggregates made by Examples I-XXI of my application Serial No. 189,282, which is hereby incorporate-d by reference. These foam aggregates are all substantially noncrushable under the given pressure, whereas the perlite crushes to a powder.

The following examples illustrate the formulae of other lightweight aggregates besides the mixture of fired foam aggregate and expanded perlite of Examples I to IV.

Example V The mixtures, Examples V and VI, were both power pressed at 50 pounds per square inch pressure to a 9 x 4 /2 x 2 /2" size brick and fired as indicated above.

Example VII Kaolin Foam Aggregate:

on gr 100 on 35 mesh gr 235 35 mesh and fines gr 100 Kaolin (raw clay) gr 325 Diatoma-ceous earth (raw) gr 240 Water cc 160 Fired 2500 F.

Wt./cu. ft lbs 36 Shrinkage percent .02

5 Example VIII Kaolin Foam Aggregate:

Cold crushing strength p.s.i. lbs 355 In the Examples VII and VIII kaolin foam aggregate is specifically the fired aggregate made in accordance with Example XI of Serial No. 189,282, filed April 23, 1962, but other fired foam aggregates shown in this application and others known to the art can also be used.

In all the examples the perlite or diatomaceous earth sacrificial aggregate can be replaced by other lightweight aggregates of similar ease of crushability. One sacrificial aggregate which had been found particularly satisfactory for this purpose, can be made by lightly calcining the unfired foam aggregate of application Serial No. 189,282, or by waterproofing the dried foam without firing.

For example, the composition of Example XXI of Serial No. 189,282 was made up, the foam generated in the slurry, and the raw starch added. This foam was lightly fired at 2000 F.

In the following examples the foam aggregate in all cases is the foam aggregate of Example XXI of Serial No. 189,282 unfired, lightly fired, or hard fired (2900 F.) as indicated.

Example 1X Hard fired foam aggregate:

7 on V mesh gr on 35 mesh gr 110 35 mesh and fines gr 55 Kaolin clay (raw) gr 300 Sacrificial aggregate and fine (Example XXI lightly fired 2000 F.) gr 500 Water cc 350 Brick were fired to 2500 F. Wt./9" straight lbs 2.4 Shrinkage percent -3.0

The same Formula XXI of Serial No. 189,282 was also made up and waterproofed by adding 10 percent pulverized pitch and 10 percent creosote oil to the foamed mix. When dry, this foam aggregate was both strong and water resistant.

Example X The following brick was made up using Example XXI of Serial No. 189,282, waterproofed as a sacrificial aggregate.

Hard fired foam aggregate:

The process was carried out as in Example I with the same formula. In the manufacture of insulating A tile which are a T-slotted shape measuring 3" x 10" x 10 /2, the T slot is used to suspend the tile in a flat arch of a furnace. Strength is needed in the T slot but minimum weights are best in the rest of the tile for better insulation and low heat storage. Slight bank filling of the press cavity shows this remarkable increase in strength without materially affecting the density of the.

rest of the tile. obtained:

The following Table II shows the results TAB-LE II.IMPROVED STRENGTH OF A TILE T SLOT I Breaking Strength of T Weight Per Slot in Pounds Percent Tile in Strength Pounds Increase Regular Fill Bank Fill The advantages of this invention are obtained largely through the use of sacrificial aggregates capable of movmg a hght aggregate to form a uniform. product under pressure. For example, the .much higher fiowability and 7 lower bulk densities of the press mixes containing sacrificial aggregates allows bank filling of the mold cavity at unequal levels. In this the densities of the pressed specimen can be altered from one end to the other,:.

placing as much as 80 percent of the entire mix in less than 50 percent of the mold area. This unexpected result has allowed the opening of an entirely new field in the manufacture of insulating products. There can now be pressed an insulating brick with a hard wearing surface which is abrasive resistant.

There can also be used this unusual property to strengthen points in the shape which need greater strength than the rest of the insulating block. An example of this is the T slots on suspended arch tile.

I claim:

1. The method of forming a lightweight refractoryshaped article which comprises mixing together a first lightweight refractory aggregate having a density of less than 50 pounds per cubic foot, water, and a second refractory aggregate which is crushable at a pressure below that at which said first aggregate is crushable, and

pressing the mixture into a shaped article at a pressure such as to crush said second aggregate.

2. The method of forming a lightweight refractory shaped article which comprises mixing together a lightweight refractory aggregate of the group consisting of fired foamed refractory particles, expanded blast furnace slag, and expanded shale; water, a bonding clay, and a second aggregate which is crushable'at below the pressure at which said first aggregate is crushable, pressing the mixture into a shaped article at a pressure such as tocrush said second aggregate without crushing the first aggregate, and firing the shaped article at a temperature.

Formerly, it're-, quired two separate products to obtain these results.-

7.-The process of claim '1 wherein the first lightweight. aggregate is a fired'foamed refractory and the: second aggregate is expanded perlite..

8.-The method .of. forming a lightweight; refractory brickcomprisingthe steps of mixing together a light. weight fired, foamed refractory aggregate and a bonding clay, with'expanded perlite ,and. water said lightweight.

fired, foamed refractory aggregate being crushableat a "pressure greater than that at which said perlite is crushable, and power pressing-the mixture within apressure range of 28 to 148 pounds per square inch directly to the desired final size and shape.

9. The method of forming a lightweight refractory brick comprising thesteps ofamixing together approximately'46' percent to;56 percent by weight of a fired foamed lightweight refractory aggregate, approximately;

6 percentto 16 percent of perlite and approximately .8 percent to 42" percent water said lightweight fired, foamed refractory aggregate being crushable at a pressure greater than that at which said perlite is crushable, and power pressing. the mixture in a pressure range of 28 to 148 pounds per square inch directly to the desired size and shape.

10. 'The method of claim 9-'wherein the fired refractory aggregate is the aggregate formed by mixing a lightweight aggregate comprising a fired refractory foamed mass, said mass being formed by mixing a substance selected from the group consisting of=kaolin, kyanite, zircon, and alumina with water and a gellingagent, adding a foaming agent, agitating the mass to obtain a foamed slurry, heating the slurry togel the foam structure within the; slurry, and firing the gelled slurryat a temperature of betweenapproximately 2500" Fiand 3000 F.

11. The method of. forming a lightweight refractory shaped article having a portion of said article of greater strength than the remainder of said article which method,

comprises mixing together a lightweight refractory aggregate, a minor amount of water, anda second aggregate which is crushable at below the pressure vat which said first aggregate is crushable to form a mixture, pressing 'the mixture into a shaped article by subjecting. one surface portion of the mixture to a higher pressure than the pressure on an adjacent surface portion, the higher pressure being sufiicient to. crush both the first and second 13. The method of claim 11 wherein the difference in pressure is obtained by applying to the mixturea piston having only a portionof a contact surface flush with the surface of the mixture when first contacted.

References Cited by the Examiner UNITED STATES PATENTS 1,929,425 *10/193 3 Hermann. 2,583,292 1/1952 Bowen et a1. 264128 3,008,842 11/1961 Miller 10 6-60 XR.

ROBERT F. WHITE, Primary Examiner.

J. A. FINLAYSON, Assistant Examiner. 

1. THE METHOD OF FORMING A LIGHTWEIGHT REFRACTORY SHAPED ARTICLE WHICH COMPRISES MIXING TOGETHER A FIRST LIGHTWEIGHT REFRACTORY AGGREGATE HAVING A DENSITY OF LESS THAN 50 POUNDS PER CUBIC FOOT, WATER, AND A SECOND REFRACTORY AGGREGATE WHICH IS CRUSHABLE AT A PRESSURE BELOW THAT AT WHICH SAID FIRST AGGREGATE IS CRUSHABLE, AND PRESSING THE MIXTURE INTO A SHAPED ARTICLE AT A PRESSURE SUCH AS TO CRUSH SAID SECOND AGGREGATE.
 11. THE METHOD OF FORMING A LIGHTWEIGHT REFRACTORY SHAPED ARTICLE HAVING A PORTION OF SAID ARTICLE OF GREATER STRENGHT THAN THE REMAINDER OF SAID ARTICLE WHICH METHOD COMPRISES MIXING TOGETHER A LIGHTWEIGHT REFRACTORY AGGREGATE, A MINO AMOUNT OF WATER, AND A SECOND AGGREGATE WHICH IS CRUHABLE AT BELOW THE PRESSURE AT WHICH SAID FIRST AGGREGATE IS CRUSHABLE TO FORM A MIXTURE, PRESSING THE MIXTURE INTO A SHAPED ARTICLE BY SUBJECTING ONE SURFACE PORTION OF THE MIXTURE TO A HIGHER PRESSURE THAN THE PRESSURE ON AN ADJACENT SURFACE PORTION, THE HIGHER PRESSURE BEING SUFFICIENT OT CRUSH BOTH THE FIRST AND SECOND AGGREGATES IN THE UNDERLYING PORTION WHERE THE HIGHER PRESSURE IS APPLIED, AND THE LOWER PRESSURE BEING SUCH AS TO CRUSH THE SECOND AGGREGATE WITHOUT CRUSHING THE FIRST AGGREGATE. 